Effects of Cementitious Amendments on the Mechanical Strength and Hydraulic Conductivity of Mine Tailings for Reclamation Cover Systems

Tailings storage facility (TSF) reclamation commonly involves the construction of cover systems, requiring large volumes of materials with specific hydro-geotechnical properties. When suitable materials are not locally available, their extraction and transport can generate significant environmental and economic costs. On abandoned or inactive TSFs, where long-term acid mine drainage may occur, reclamation is highly sensitive to geochemical conditions, especially for weathered tailings affected by indirect oxidation and secondary mineral precipitation. Using these tailings as cover materials represents a promising alternative but would require improvement of their mechanical performance and limitation of metal leaching. This study investigated the effectiveness of general use limestone (GUL) and slag-based cements, a combination of GU and ground granulated blast furnace slag (GGBFS), for the solidification/stabilization of weathered tailings to create a hydraulic barrier. Cemented paste mixtures incorporating 5–7 wt% binder were evaluated through unconfined compressive strength (UCS), saturated hydraulic conductivity (ksat), and mineralogical analyses. The addition of binder significantly increased mechanical strength and reduced ksat, with UCS > 1000 kPa and ksat < 1 × 10−9 m/s, generally achieved after 28 days of curing with 7 wt% binder. Performance depended on tailings geochemistry: slag-based cement (20GU/80GGBFS) performed better in tailings with neutral paste pH, while GUL yielded higher UCS in acidic tailings. Very limited hydrate formation was observed: mainly ettringite in GUL-treated sulfate-rich tailings and C–S–H in slag-treated mixtures. These results demonstrated that cementitious treatment of TSFs could be an efficient, if binder type and dosage are adapted to site physical and geochemical variability of weathered tailings.